High pressure, high temperature (“HPHT”) sintering processes include using a high-pressure press, such as a cubic press, a belt press, or a toroid press, to subject a material or material mixture to high pressure and high temperature conditions. The material may be held within a container that is placed inside the press, where both the material and the container are subjected to HPHT conditions. The container should be sufficiently deformable to transmit pressure to the material being pressed, but must also be strong enough to seal the central compartment in which the material being sealed is held so that high pressure can be developed within the central compartment. In some processes, an insulating sleeve, made of a low thermal conductivity material, is assembled between the container and the material being pressed to reduce heat dissipation through the container.
When used to sinter ultra-hard materials, such as polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (PCBN), a high-pressure press may apply pressures in the range of 5 to 8 GPa and temperatures in the range of 1300 to 1650° C. Some processes may include sintering the ultra-hard material to a substrate, such as a carbide substrate, for example, during a single sintering process for forming the ultra-hard material body and bonding the ultra-hard material body to the substrate, or using separate sintering processes for forming the ultra-hard material body and bonding the ultra-hard material body to a substrate. However, some materials may be pressed under a pressure of greater than 8 GPa and a temperature greater than 1650° C. For example, a binderless nano-polycrystalline PCD material may be sintered in a high-pressure press at a pressure of about 15 GPa and a temperature of about 2300° C.